Many wood stove, fireplace and other fuel combustor manufacturers claim to have high burning efficiency and the capability of heating large spaces. While it is relatively easy to design a stove or a fireplace insert that is capable of efficient operation at a particular burning setting, it is very difficult to provide such a burner that is capable of efficient operation over the full range of burn rates. Additionally, it is difficult to provide a burner such as a wood stove that is not only efficient over the entire burning range, but that provides emissions, including particulate material, that meet the Environmental Protection Agency requirements. To meet the Environmental Protection Agency requirements and state agency requirements, such as the stringent requirements set forth in Oregon and Colorado, many stove manufacturers have included catalytic combustors to finalize the burning process and thereby prevent emission of particulate materials and gases beyond the required levels. While such catalytic combustors operate effectively during certain conditions, they can become fouled or otherwise rendered inefficient, especially when other than selected materials are burned within the associated stove or fireplace. Additionally, the catalytic combustors are quite expensive and must be periodically replaced. It therefore becomes very desirable to obtain a combustor that will meet stringent air quality standards without the aid of a catalytic combustor, and that will operate over a complete range of burning conditions with consistent, repeatable low emission.
The above object has been met by the wood stove disclosed in U.S. Pat. No. 4,766,876. This patent discloses a wood stove with features primarily relating to the mixture of air with burning and unburned gases to reduce emissions to stringent requirements. While this stove operates effectively, it remains desirable to lower emission rates even further.